WOLLASTONITE  , a

rock-forming mineral consisting of calcium metasilicate, CaSiO3, crystallizing in the monoclinic system and belonging to the pyroxene (q.v.) group . It differs, however, from other members of this group in having cleavages, not parallel to the prism-faces, but in two directions perpendicular to the plane of symmetry . Crystals are usually elongated parallel to the axis of symmetry and flattened parallel to the ortho-pinacoid, hence the early name " tabular spar "; the name wollastonite is after W . H . Wollaston . The mineral usually occurs in white cleavage masses . The hardness is 5, and the specific gravity 2.85 . It is a characteristic product of contact-metamorphism, occurring especially, with garnet, diopside, &c., in crystalline limestones . Crystals are found in the cavities of the ejected limestone blocks of Monte Somma, Vesuvius . At Santa Fe in the State of Chiapas, Mexico, a large rock-mass of wollastonite carries ores of gold and copper: here are found large pink crystals which are often partially or wholly altered to opal . (L . J .